Process for carbonizing carbonaceous materials



Dem 1934- w. w. ODELL 1,983,943

PROCESS FOR CARBONIZING GARBONACEO Filed Dec. 1'7, 1929 US MATERIALS l T 1 1 9 i I 8 l J i INVENTOR.

A TTORNE Y.

Patented Dec. 11, 1934 UNITED STATES PATENT OFFICE PROCESS FOR CARBONIZING GABBONA- I CEOUS MATERIALS The invention relates to the process of carbonizing subdivided solids by introducing them in a stream, regularly or intermittently, into a fluidized mass of heated solids of small size, with the possible recovery of by-products from carbonization. Briefly, the process consists in fluidizing a mass of finely divided solids, which may include or comprise, coke, coal or other solid combustible matter, in a. closed chamber, by causing the passage of an aeriform fluid therethrough, heating said mass by a suitable application of heat as herein completely described, and, while the mass is still hot and in the fluidized state, introducing the material to be carbonized in a state of suitable subdivision, meanwhile, continuing the passage of said aeriform fluid through the whole.

Some of the objects of this invention include the following: v

(l) The absolute control of the temperature of carbonization without sacrificing capacity (through put per unit of time.)

v (2) Control the rate of heating of the material in process eificiently, without large capital investment and without sacrificing capacity.

(3) The recovery of a high yield of by-productsincluding condensable matter from the materials in process. Y

(4) Decrease the heat losses, and-the amount required in processing.

(5) Decrease thetime required for carbonizing.

(6) Lower the cost of processing coal shale and similar substances.

('7) Increase throughput of materials per unit of investment.

(8) Decrease the amount of complete cracking of the condensable matter evolved during carbonization.

(9) Make possible the carbonization of smallsfzed solid fuel commonly wasted at mines because low priced equipment having a high throughput capacity is not available.

(10) Provide a single process wherein a fuel can economically be carbonized at high or low temperature by directly applied heat.

(11) Expel volatile matter from solids or liquids rapidly at a predetemiined and controlled simultaneously herewith for A process of treat-- ing materials, Serial No. 414,710, which describes broadly the general features of the process and shows apparatus in which it may be conducted.

In the carbonization of coal, lignite, shale and other carbonaceous materials, the matter of transfer of heat into the materials in process is 5 one offering numerous obstacles particularly when high thermo-efliciency is desired or when it is essential to recover a maximum yield of condensable by-products. In the carbonization of many materials, it is often essential to prevent overheating of portions, of the material bein processed. It is common practice to conduct carbonization in refractory apparatus, transferring the heat through a non-conductor, or rather a poor conductor, to the material being processed. Because therate of heat transfer and therefore the capacity to carbonize depends upon the difference in temperature between the inner and. outer walls of the carbonizer it has been found to be economical and in many cases necessary to maintain a high temperature on the outside of the refractory carbonizer-wall in order to maintain a throughput per unit of time compatible with the cost of construction and the cost of operating the carbonizer. Thus it is common to flndthat equipment originally designed for the low-temperature carbonization of solid fuel can be more economically operated at high temperatures because a greater throughput is thus obtained, the yield of condensable by-products is usually materially reduced by this procedure. It appears to be uneconomical to carbonize solid fuels at a definite temperature by heating them when retained in a refractory chamber by the external application of heat. This is more particularly true in the low-temperature carbonization of fuels, that is at temperatures of 500, 600, 700 or 800 centigrade. The maximum yield of condensable by-products is obtained only when over-heating of the fuel is prevented, so far as I am aware. In the commonly employed equipment for carbonizing fuels, it is dimcult to heat the center of the individual pieces of the fuel being processed without over-heating their outer surfaces. Whenv the fuel is crushed to fine sizes for the purpose of eliminating this difllculty the whole mass functions as a heat insulator, the outer portions, that is those contacting the hot wall are usually heated to a high temperature before the inner portion of the mass has been heated above Centigrade. Attempts to overcome this difficulty by slowing the rate of heating (the rate of application of heat energy) have resulted, so far as I am aware, in a 7 prohibitive increasein the cost of the canbonizers 66 per ton-day of throughput. Other attempts to surmount this difficulty include: (1) decreasing the thickness of the mass of fuel being treated; (2) passing the suitably crushed fuel through the hotzone while retained. on metal supports. So far as I am aware these and similar efforts have-not been entirely satisfactory either from an economical or a technical viewpoint. It is believed that because of heat transfer difliculties chamber, at a velocity adapted to cause them toremain in a state of motion suspended in said fluid within said chamber, the mass being in a fluidized condition having the appearance of a boiling liquid, and introducing therein at a controlled rate suitably sized solid fuel. The solids may be comprised of the fuel to be treated, a carbonization product thereof or other materials; they may be combustible or non-combustible, catalytic or non-catalytic to the reactions involved. The fluid used in maintaining the mass of solids in a fluidized state, preferably an aeriform fluid, may comprise combustion gases, inerts, an oxygen-containing gas, a mixture of a combustible gas with an oxygen-containing gas or other fluid. The fuel added to the fluidized mass may be discharged therein at a continuous rate or intermittently and the state of fluidity may be maintained until the desired state of carbonization has been reached or it may be discontinued before that degree of carbonization has been obtained. It is necessary or at least preferable in the operation of my process to maintain the upward velocity of the fiuidizing medium (the fluid) greater than a definite iv velocity as long as the mass is maintained in afluidized state. This minimum velocity varies according to the average size of particles of the solids, the density of the matter comprising the particles, density of the aeriform fluid used, and other factors but may be defined as the lifting velocity, namelythe velocity required to lift the particles against the force of gravity. Considering the particles of the solids to be spheres the minimum velocity may be approximated by the mathematical formula where V=velocity of the aeriform fluid expressed in centimeters per second, R=the average radius of the solid particles fluidized, in centimeters,

D=density of the solid material comprising the particles, d=density of the aeriform fluid, and

G=acceleration due to gravity, expressed inC- l G. S. units. A velocity of flow very much greater where the finer sizes are blown out of the fluidized mass, entrained in the'fluid.

Figure 1 showsdiagrammatically in elevation one form of apparatus in which my invention may I control valve 13, a gas inlet 14 having control valve 15, discharge 16 for removing solids that are, as confined in 1, in a fluidized state, with control valve 17, base discharge 18 with control valve 19, and a cleanout or secondary discharge door 20. The mass of fluidized solids is shown at 21. Although I depend upon internal heating in operating with my process, it is recognized that the heat capacity of most aeriform fluids is low. This of course means that large volumes of gas. (fluid). must be circulated through the mass of material being processed in order to impartthereto a quan. tity of heat equivalent to that evolved during the combustion of a relatively verysmall volume of fuel. One means of supplying the necessary heat includes the circulation of an oxyq gen-containing gas through the fluidizedmass, maintaining controlled combustion therein. In this instance the heat required may be, derived from the combustion of a portion of the solid fuel existing in the fluidized state. may comprise a combustible gas and an oxygen containing gas mixed in. definite proportions for the purpose of supplying a definite quantity .of; heat to the fluidized solids; in this instance the combustible gas is burned in supplying the necessary heat. The heat may be supplied electrically and internally by the use of a magnetic core or,

other means known in electrical engineering practice. Attention is called to the fact that-the objections cited against heating .extemally through refractory walls do not apply to the latter method of heating because the materials in process are in a constant state of motion and the mass being fluidized does not function as aheat insulating medium. Although it is possible to carbonize materials by applying heat internally, externally or both internally and externally, with or without combustion occurring in the fluidized mass I prefer not to limit myself to a particular method 'of heating. It is mybelief that the process irrespective of the method of heating patentably new. In other .words Ibelieve itis new to admix fuel in a fine state ofdivision into a fluidized mass of heated, finely divided, and preferably sized, solids through which-a fluid is caused to pass andcarbonize it within said mass.

of heated solids, or substantially in contact withit. 1

In my process I usually prefer to employ sized solidshaving an average diameter of A; of an inch to inch although larger or smaller sizes may be used satisfactorily. Frequently it is preferable that the solids comprise solid fuel such as petroleum coke, charcoal, coke, anthracite coal or other carbonaceous material. When one or more of these materials is used as the fluidized mass my process the heating operation and the temperature is readily controlled by controlling the amount of oxygen-containing gas circulated through the mass, or by controlling the amount. of combustible gas and oxygen circulated The fluid there through. When it is intended to carbonize coking fuels it is preferable to introduce them into the fluidized mass in a state of flneness substantially equal to or less than that of the fluidized solids. When a large quantity of coking fuel is rapidly admitted to a mass of heated fluidized solids and the flow of fluid (the fluidizing medium) discontinued shortly thereafter the coking fuel upon carbonizing will form a solid mass with the said solids dispersed therein. The degree of coking will obviously depend upon the amount of heat supplied to the coking fuel and this in turn will depend upon the duration. of the flow of the fluidizing medium after the addition of said coking fuel, and upon therelative masses of said fuel and said fluidized solids. When it is desired to make a product of this nature, a homogenous mass is obtained when the fluidized solids comprise smallpieces of 'coke resulting from the carbonization of the fuel treated. However when it is desirablejto use non-coking coals in the production of a coke the result may be attained by fluidizing said non-coking fuels in a suitable chamber with a suitable means for applying heat and introducing therein, rather rap idly, the predetermined quantity of suitably crushed coking fuel, continuing the application of heat and the flow of the fluidizing medium for a period of time found by experiment to be desired and then discontinuing the flow of fluid'zing medium with or without the discontinuance of the application of heat and forming by the oementing action of the coking fuel a solid mass comprising substantially a coke. When this result is desired the coke is of better quality with respect to friability when the average size of the particles of the "coking fuel used in smaller than that of the fluidized solids. When it is desired to prevent the cementationof the fuel and the fluidized solids into a solid mass the sized'fuel should be introduced into the fluidized mass at a moderately slow rate, preferably continuously, with the simultaneous application of heat.

I flnd that a fluidized mass of solids behaves much like a liquid with respect to bouyant action upon solids introduced therein; that is, when sized solids of greater specific gravity than that of the solids fluidized are introduced into the fluidized mass, they tend to sink therein, whereas materials having a lower specific gravity than that of the fluidized solids float thereon or remain in a fluidized condition close to the surface. Thus when coal is introduced into a mass of fluidized hot coke it flrst tends to sink, but subsequently upon being heated and when evolving gas it again tends to rise in the fluidized mass. This circulation is beneficial in maintaining a uniform temperature throughout the mass. It is important to note that when the fluidized solids have a much greater density than the fuel to be processed the fuel will not only remain on top of the fluidized solids but said solids will leave the fluidized condition settling in a substantially rigid mass at the bottom of the treating chamber when the rate of flow of the fluid therethrough is reduced, the coal remaining in the fluidized state above it. This I take x 3 erated utilized in the fluidized fuel above it by using the proper fluidizing agent.

It is understood that, in passing a fluid up- 'wardly through the fluidized mass of solids, or

carbonaceous material, its composition may be changed at will during the course of carbonization. Fpr example during the early stage of carbonization, or ina period just prior thereto when the solids are being heated, the fluid may be comprised of combustible gas and some oxygen, whereas at a later period the oxygen content may be reduced to zero, or almost to zero, and steam or other fluid may be substituted for the gas, or combustible gas alone may be used. Contrarywise, the steam may be used in the early stage of processing the carbonaceous material and the oxygen-containing gas at a later stage or the steam may be used throughout the process. Again, the temperature of the steam or other fluid used may be changed at will during the process either by preheating or by employing an oxygen-containing gas such as air in admixture therewith in amounts varying under control during processing. After the fuel reaches a certain temperature, autoxidation takes place rapidly accompanied by rising temperature and thus the rate of carbonization and temperature attained in the mass can readily be controlled by controlling the oxygen content of the fluid. The exothermic reaction may be insipient combustion of the carbonaceous material, true combustion of it, combustion of gases in contact with it or combinations of them. This control of temperature permits the production of a product carbonized at so low a temperature that it can be removed from the reaction chamber in a condition suitable for molding or briquetting without a binder thus making a dense fuel. The application of pressure to the material heated to a moderate temperature produces a dense fuel. The form of apparatus used for this purpose is immaterial to this application although it is recognized that the mass can readily be compressed in the reaction chamber and fluidized product, CO2, stack gas, steam or other fluid may be used but it is frequently preferable to pass steam through one chamber as a cooling agent and used the steam thus heated in heating the material in a different (separate) chamber.

When tarry matter is introduced into a fluidized mass of carbonaceous material as a component of the fluid, or otherwise, it is not only carbonized but the distillation products are recoverable in the exit gas. Similarly powdered pitch may be carbonized by my process; in this instancee'it preferably is not a part of the fluidizing medium. I

Using oil-shale as the carbonaceous material it may be treated as follows: Start the operation by fluidizing a sized coke or other fuel having an average particle size of about V or of an inch in diameter using air as the aeriform fluid and fluidizing medium. A fire 'is kindled in the mass and air-blasting continued. After the fluidized mass of fuel is heated to a desired temperature the crushed and preferably sized is a pseudo-liquid, and air-blasting is discontinued. Steam and other gases are now used as the chief components of the fluidizing medium. After the volatile matter is largely expelled from the shale the air-blasting is continued, heating the mass by burning the carbon in the shale residue. The cycle is repeated but some of the residue is removed periodically. If it is desirable to sacrifice yield of oil for high capacity the air may be used continuously with steam, merely by varying the proportions as desired in various phases of the process; using more air for higher temperatures and more steam for lower temperatures and more steam-distillation. The process becomes continuous when the shale is slowly but substantially continuously added to the pseudo-liquid and the residue withdrawn substantially continuously. The solid fuel need be used only when starting the operation. It is not necessary to use steam but it is preferable to use it. Certain coals may be treated in this same manner, particularly non-coking coals or the so called non-coking coals.

When using coking coal and when the average size of the pieces introduced into the fluidized mass is rather large, larger than to inch, there is a tendency for large pieces of coke to form even though the mass is apparently in a fluidized state. The lumps form probably by combination during the collisions in the pseudoliqu'id when the particles are in the plastic stage. These pieces tend to collect at the bottom, and if the velocity of the fluid is not,excessive, they leave the pseudo-liquid, that is they settle out and are no longer in the fluidized state. These pieces of coke are denser than ordinary coke made by heating the same coal in a retort.

I find that when a quantity of coking coal is rather rapidly introduced into a fluidized mass of heated coke, the particles of coal being smaller than those of the coke, and the whole maintained in the fluidized state for a brief period simultaneous with continued heating and then allowed to settle before coking has occurred, a mass of coke forms that upon' breaking does not form flngers,-flnger coke The term substantially carbonized as used in the claims refers to a carbonaceous material that has had volatile matter expelled from it by the application of heat, and not necessarily to a completely carbonized product. When it is desirable to treat coal at 300 or 400 C. and remove the product it is considered to be carbonized, as the word is used in the, claims. In treating fuels for briquetting it is desirable to heat them to a predetermined maximum temperature in order to prevent the formation of abrasive char; in such cases the char is not a completely carbonized product but it is considered to be carbonized.

The term fluidized mass as used herein and in the claims does not refer to a gas containing entrained particles of solids, such as is formed when a powdered fuel is air-blown into a furnace for combustion; it is a pseudo fluid such as is formed by passing an aeriform fluid uptrained in the aeriform fluid but are in vibrant motion; the pseudo liquid (fluidized mass), havshale is slowly introduced into the mass which ing a density much greater than that of the same aerlform fluid with entrained particlesbf the same kind of solid. Thus in a fluidized mass the lineal motion of the particles is much less than that of the particles entrained in agaseous medium and likewise the concentration-of the particles (mass per unit of ,volume) is greater in the former than in the latter instance. The "fluidized mass" may be produced by thevelo'city effect of blasting a stationary bed of solids (preferably uniformly sized solids) with an aeriform fluid at such a rate that the particles of "said solids assume limited motion without being en-- trained in said fluid; the fluid passing continuously upwardly through said mass of solids. This differentiates my fluidized mass from' other forms of suspensions. The almost obvious bnefltde rived from the employment of the dense, fluidized mass is its greater heat-carrying capacity per unit container volume than that of suspension of the same solids entrained in the fluid.

Having described my invention, and the matterthat I believe is new, I claim:

1. A process for the low-temperature carbonization of solid carbonizable material, which corn-- prises blowing air through a layer of the said material substantialiy in granular form and of considerable depth at such a rate that the said layer is maintained in a state of motion such that the layer presents the appearance of a boiling liquid, the temperature of operation being at a carbonizing temperature, and withdrawing the carbonized residue.

2. A process for the low-temperature carbonization of solid carbonizable material, which comprises blowing air in admixture with steam through a layer of the said material substantially in granular form and of considerable depth at such a rate that the said layer is maintained in a state of motion such that the layer presents the appearance of a boiling liquid, the temperature of operation being at a carbonizing temperature, and withdrawing the carbonized residue.

3. A process for the low-temperature carbonization of solid carbonizable material, which comprises blowing a stream initially comprising essentially premixed air and combustible gas through a layer of the said material substantially in granular form and of considerable depth at' such a rate that the said layer is maintained in a state of motion such that the layer presents the appearance of a boiling liquid,'the temperature of operation being at a carbonizing temperature, and withdrawing the carbonized residue.

4. A process for the low-temperature carboni zation of solid carbonizable material which comprises blowig a stream initially comprising es sentially premixed air and combustible gas along with steam through a layer of the said material layer presents the appearance. of a boiling liquid the temperature of operation being at a carboniz-' ing temperature and withdrawing the carbonized residue.

5. A process for the low-temperature carbonization of solid carbonizable material, which comprises blowing a gaseous stream initially com prising essentially premixed air, steam and combustible gas through a deep layer of the said material the particles of which are substantially oneeighth of an inch to one-half an inch in diameter at such a rate that the said layer is maintained in a state of motion such that the layer presents the appearance of a boiling liquid, the temperature of operation being at a carbonizing temperature and withdrawing the carbonized residue.

6. A process for carbonizing solid carbonizable materials, comprising, passing a gaseous stream initially comprised essentially of premixed air and combustible gas, upwardly through a confined layer of carbonizable material substantially in granular form and of considerable depth at such a rate that said layer is maintained in a state of motion such that the said layer presents the appearance of a boiling liquid, maintaining the temperature of said material at a carbonizing temperature by the oxidational combustion of said gas by said air in said stream, and withdrawing the carbonized residue.

'7. A process of carbonizing solid carbonizable materials, comprising, passing a stream of an aeriform fluid initially comprised essentially of premixed air and combustible gas upwardly through a confined layer of solid fuel in substantially granular form and of conslderable depth at such a rate that the said layer is maintained in a state of motion such that the layer presents the appearance of a boiling liquid, promoting combustion of said gas in said stream thereby heating said material to incandescence, introducing into the fluent heated mass a carbonizable solid material in a state of subdivision similar to that of said granular fuel meanwhile maintaining the solids in the fluent state carbonizing said material, discontinuing the combustion reaction and removing the carbonized residue.

8. The process of treating carbonizable solid fuels with the recovery of the carbonized product, comprising, heating a confined, considerably deep layer or finely subdivided solid carbonaceous fuel to incandescence, passing a gaseous stream initially comprising premixed air, steam and combustible gas upwardly through said layer at such a velocity that the said layer is maintained in a state of motion such that the layer presents the appearance of a boiling liquid, introducing into the incandescent layer while in said state of motion a finely subdivided solid fuel to be carbonized, maintaining the whole mass in similar fluent state for a period by virtue of said stream velocity carbonizing the latter fuel while in the fiuent state and evolving gas, withdrawing and recovering the carbonized fuel separate from the gas.

9. The process for the low-temperature carbonization of carbonizable solid fuels, comprising, confining in a reaction chamber a considerably deep layer of coke in a state of fine subdivision theparticles having an average diameter of about to inch, passing an aeriform fluid stream initially comprised essentially of premixed air and combustible gas upwardly through said layer at such a rate that said layer is maintained in a state of motion such that the layer presents the appearance of a boiling liquid, burning said gas in said stream while passing through said layer heating said coke to a carbonizing temperature above 400 C., introducing into the heated layer of coke, in a similar state of subdivision, the solid fuel to be carbonized, maintaining the whole mass of solids in a similar fluent state for a period by virtue of the velocity of said stream, heating said solid fuel to a temperature above lOO C. substantially carbonizing it at least in part by the transfer of heat from the heated coke, withdrawing and recovering the substan-' tially carbonized solid fuel.

WILLIAM W. ODELL. 

